Local area networks (LANs) are essential for networking a plurality of computers, servers, printers, and the like. In particular, since recent years have seen the achievement of standardization of 1000BASE-X (IEEE802.3z) and 1000BASE-T (IEEE802.3ab), Ethernet (registered trademark) LAN technologies have been playing the leading role in the age of high-speed multimedia networks.
Such a LAN can use fiber optic cables to extend its transmission distances. That is, the transmission distance can be extended by providing media converters each at both ends of a link between adjacent nodes to couple a fiber optic cable to a metal cable.
Recent years have also seen the spotlight on the FTTH (Fiber To The Home) which employs fiber optic cable lines extended to each home to freely exchange music, moving images, medical data or the like over the high-speed line. The advent of the FTTH age would require a media converter for connecting a fiber optic cable line to the metal cable of a computer in an office or at home. Thus, the media converter is an essential communication device for use with high-speed multimedia networks to come.
In general, the media converter includes physical layer devices each provided at a port for connecting to a fiber optic cable and a port for connecting to an UTP (Unshielded Twisted Pair) cable. Each physical layer device supports the MII (Media Independent Interface) specified in the IEEE802.3 standard.
Such a property of the media converter requires that the UTP cable and the fiber optic cable should be regarded as one cable including the media converter, and devices to be connected are often installed apart from each other. Accordingly, those generally employed have a missing link function of automatically disconnecting one link when the other link is disconnected. For example, when power is turned off or some trouble occurs causing the UTP cable device to be disconnected, the media converter automatically disconnects the fiber optic cable link.
When such a media converter is used to connect the UTP cable to the fiber optic cable, it is critical to properly exchange line abilities with each other in order to provide assured flow control. In particular, since the Gigabit Ethernet network is based on auto negotiation with a link partner to thereby set the optimum transmission mode, no flow control can be ensured without properly transferring line abilities. For example, to connect two devices of different abilities to each other, it is necessary to go through auto negotiation to know mutual abilities in order to set to the lower ability.
According to the Gigabit Ethernet standard for employing the fiber optic cable, the remote fault function can be used to send a link disconnect request to a device coupled with a fiber optic cable. The remote fault signal is held in a configuration packet and sent to a link partner during the auto negotiation on which the Gigabit Ethernet is based.
However, the link disconnect method utilizing the remote fault function has several problems. First, as described above, since the remote fault signal is contained in the configuration packet during the auto negotiation, the remote fault function is operable only between devices that are compatible with auto negotiation. Naturally, the remote fault function is not operable in the manual mode.
Secondly, some communication devices interpret the remote fault function in a different way, possibly resulting in the link disconnect request being not properly interpreted. For example, some devices interpret that the request does not mean a link disconnection because the remote fault signal being properly received indicates a proper connection between the devices. For this reason, in some cases, a link may not be disconnected using the remote fault function.
Thirdly, as a transitory problem, some earlier devices have not incorporated the remote fault function because the Gigabit Ethernet standard itself is a new one. A mixed device network incorporating such a device as having no remote fault function cannot ensure the disconnection of a link using the remote fault function.
It is therefore an object of the present invention to provide a link disconnection method that ensures link disconnection of a communication device having no remote fault function and a media converter having such a link disconnection function.
It is another object of the present invention to provide a media converter which can properly exchange line abilities and a method for auto negotiation in a network using the media converter.